What is Oil Fish and Escolar?
Oilfish, scientifically known as Ruvettus pretiosus, and its close relative Escolar (Lepidocybium flavobrunneum), are two species of snake mackerel known for their rich, buttery flavor. The alluring taste, however, comes with a significant and unpleasant catch. A large portion of their body weight, sometimes up to 25%, is composed of a unique, indigestible fat called wax esters. This fatty substance, also known as gempylotoxin, is what provides the fish its desirable texture but is impossible for the human body to properly digest. These fish live in deep tropical and temperate waters, accumulating this particular fat from their diet. Unlike the beneficial omega-3 fatty acids found in other oily fish, the wax esters in oilfish pass through the digestive system unchanged, leading to severe discomfort.
The Indigestible Wax Esters
The core issue with oil fish lies in its biology. While most animals can break down and absorb fats, humans lack the specific enzymes required to metabolize the wax esters found in these fish. As a result, when consumed, the oily substance travels through the digestive tract and accumulates in the rectum. Due to its low melting point, it can spontaneously leak, causing a condition known as keriorrhea. This is not a form of food poisoning caused by bacteria or a toxin, but rather a direct physiological reaction to the un-metabolized fat.
The Unpleasant Digestive Consequences
Consumption of oil fish can lead to a variety of gastrointestinal issues, with the most notable being keriorrhea. Symptoms typically appear between 30 minutes and 36 hours after eating and, while distressing, are generally not life-threatening. The effects usually subside within 24 to 48 hours.
Common symptoms of oil fish consumption include:
- Oily Diarrhea (Keriorrhea): The involuntary release of an oily, yellow or orange discharge from the anus.
- Abdominal Cramps: Mild to severe stomach pain and discomfort.
- Nausea and Vomiting: A feeling of sickness that can lead to vomiting.
- Headaches: Some individuals also report experiencing headaches.
- Loose Bowel Movements: Generalized diarrhea in addition to the oily discharge.
What is Keriorrhea?
Keriorrhea is the scientific term for the oily, orange-colored stools caused by ingesting fish containing high levels of indigestible wax esters. The condition is often characterized by a strong odor and can occur without warning. It is important to distinguish this from typical diarrhea, as keriorrhea does not cause a significant loss of bodily fluids. However, the uncontrollable nature of the oily discharge can be embarrassing and highly uncomfortable for affected individuals.
How Cooking Fails to Eliminate the Risk
One of the most persistent misconceptions about oil fish is that proper cooking can make it safe to eat. Unfortunately, this is not the case. The indigestible wax esters are not broken down by heat, whether through grilling, frying, or baking. Some suggestions, such as grilling to render off the fat, may slightly reduce the wax ester content, but there is no proven method to guarantee a no-effect level. Discarding the cooking liquid and not using it for sauces is also advised, but the risk remains. For this reason, many food safety authorities recommend simply avoiding these species altogether.
Oilfish Mislabeling Dangers
A significant factor in accidental oil fish consumption is the deceptive practice of mislabeling. To capitalize on its appealing texture and appearance, some vendors and restaurants sell oilfish under more commercially desirable names.
Commonly used aliases for oilfish and escolar include:
- "White Tuna" or "Super White Tuna"
- "Hawaiian Butterfish"
- "Codfish" or "Ruddercod"
- "Butterfish"
- "Sea Bass"
- "Walu"
This mislabeling is a serious issue, as it prevents consumers from making informed choices about their food and puts them at risk of unpleasant side effects. Many food safety agencies have had to issue public warnings and guidelines to combat this practice.
Oilfish vs. Safer Fish: A Comparison
To highlight the key differences, here is a comparison between oilfish and commonly consumed safe fish like tuna and salmon.
| Feature | Oilfish / Escolar | Tuna / Salmon | Safe Fish Standard | Potential Impact |
|---|---|---|---|---|
| Fat Content | High (14-25% by weight) | Moderate to high, depending on species | Low to moderate | Significant Risk of keriorrhea due to wax esters |
| Fat Type | Indigestible wax esters | Digestible triglycerides (healthy omega-3s) | Digestible fats, easily processed | No Risk of keriorrhea |
| Digestive Effect | Strong purgative, leads to keriorrhea | Improves cardiovascular and brain health | Easy digestion, no negative effects | Adverse reaction vs. Positive health benefits |
| Safety Status | Restricted or banned in several countries | Considered safe and encouraged for consumption | High | Unsafe for most consumers vs. Generally Safe |
Health Warnings and Global Restrictions
Due to the widespread issue of keriorrhea and the problem of mislabeling, many food safety authorities around the world have issued warnings or implemented restrictions on the sale of oilfish and escolar. Countries such as Japan and Italy have banned the sale of these species entirely. In other places, like Australia and Canada, food safety guidelines mandate that sellers must correctly label the fish and inform consumers of the potential health risks. This is particularly important for sensitive groups, including pregnant women, children, and individuals with pre-existing bowel conditions, who are more susceptible to adverse effects.
Conclusion: Safer Alternatives to Oil Fish
In conclusion, the primary reason you can't eat oil fish without risking unpleasant side effects is the presence of indigestible wax esters in its flesh. This naturally occurring fat, while not life-threatening, can cause severe gastrointestinal distress, most notably keriorrhea. Cooking and other preparation methods are not effective at removing this risk. Given the common practice of mislabeling, it is often best to avoid these fish to prevent accidental ingestion. Fortunately, many safe and delicious alternatives exist that offer similar richness without the digestive danger. Choosing reputable and properly labeled fish such as salmon, mackerel, or tuna ensures you get all the nutritional benefits of oily fish without any of the risks. Always purchase fish from trusted sources and verify the species if you are unsure.
